Online ad network Turn has raised a $15 million second round funding, a spokeswoman for the company said. The Redwood City’s investors include Norwest Venture Partners, Trident Capital, and Shasta Ventures. The company, which was co-founded by former AltaVista CEO Jim Barnett, raised an $8.5 million first round from its backers in early 2005, about a year after the company began testing its ad network, the Turn rep added. The news of its funding is tied to the formal launch of its Turn Smart Network, which tries to integrate contextual, audience, behavioral and other targeting processes. More details about the unveiling of Turn’s online ad network in this release.